The present invention broadly relates to a spindle control system for use in a machine tool which automatically performs mechanical machining while making automatic exchange of tools and, more particularly, to a system incorporating a resolver and adapted to stop the spindle of the machine tool at a commanded position. Still more particularly, the invention is concerned with a system for stopping a spindle at a commanded position, improved to permit an adjustment of the stopping position.
Such machine tools are known as having automatic tool exchanging functions and are capable of automatically performing mechanical machining through automatic exchange of tools. In this type of machine tool, it is essential that the spindle be stopped precisely at a commanded position, in order that the mating portions of the spindle and the tool can smoothly engage with each other. The stopping of the spindle at the commanded position is necessary also in boring, because the boring tool cannot be correctly inserted into a bore formed in the workpiece unless the spindle is stationed precisely at the commanded position. Thus, in the field of mechanical work, there is a great demand for in the art for stopping the spindle of a machine tool precisely at a commanded position. Hitherto, a mechanical braking mechanism and a pin mechanism in combination have been used for stopping the spindle at the commanded position. This mechanical system, however, often failed to stop the spindle at the commanded position partly because of frequent breakage of the pin mechanism (stopping mechanism) due to the application of an abnormal external force or the occurrence of an extraordinary state in the machine tool and partly because of rapid wear of the braking mechanism due to friction. As a consequence, conventional machine tools often failed to perform the automatic exchange of tools and the insertion of the boring tool. In order to avoid such a failure, it has been necessary to undertake a frequent inspection of the machine tool or a renewal of worn parts.